It is well known that heat sources, such as internal combustion engines and the like, must be cooled in order to maintain operation within desired temperature ranges and ensure longevity of the item itself. Internal combustion engines, for example, generate as much as two third of the total energy produced as wasted heat, half of which must be exchanged with the surrounding atmosphere in order to cool the engine. Whilst engines can be air cooled, a radiator system is often used in which hot cooling fluid from the engine is passed through the radiator such as to allow the heat therein to be exchanged with the atmosphere before cooled fluid is returned to the engine for subsequent re-use. Sometimes the forward motion of the vehicle can be sufficient to drive cooling atmospheric air through the radiator but, at low speeds, some forced air movement from a fan arrangement may be required. The mechanical energy required to drive the fan can amount to as much as one tenth of the total energy produced by the engine and the operation of the fan can have a significant effect on the overall efficiency of the engine. In air cooled arrangements, the fan may be employed without the radiator and operated to draw or force air over the engine or an extended cooling surface associated therewith.